A very rare archaeological find—a spontaneously mummified human brain—will shed light on the genetic and social history of Bronze Age humans.

We’ve all heard of brains being “baked” or “fried,” usually in reference to drug abuse. But a boiled brain, preserved for 4,000 years?

Apparently that’s what happened in Turkey, said Dr. Meriç Altinöz of Halic University in Istanbul. Altinöz and other researchers report their analysis of four ancient human brains found in a Bronze Age settlement in western Turkey in the current edition of HOMO – Journal of Comparative Human Biology.

Altinöz told Healthline he believes an earthquake and subsequent fire transpired in the settlement where archaeologists unearthed the brains. Basically, the brains were buried and deprived of oxygen, while the heat from the fire caused them to cook inside their skulls.

The result was a remarkable preservation process called “spontaneous mummification,” Altinöz said, of which there have only been about a dozen reports since 1857.

“Two of these articles were dealing with modern samples found in an African bushveld and in an Bulgarian mass grave. Other samples were archaeological specimens, which were 500 to 8000 years old,” Altinöz said.

But since archaeologists don’t typically open fossilized skulls to look inside, brain tissue may be preserved more often than we think, Altinöz added.

Other recorded cases of spontaneous mummification were not the result of boiling. In fact, the process can occur in a variety of ways. “Though our brain samples are not the oldest, they are very unique in many aspects,” Altinöz said. “In other samples of spontaneous mummification, samples were mummified either in glaciers, due to freezing; bog sediments, likely due to toxic tannins of putrefied plants, which exerted anti-bacterial actions; and in deserts, due to dehydration.”

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Archaeologists unearthed the brains between 2006 and 2011. The most intact brain is now on display at the Turkish museum at Dumlupinar University. Fragments from the other brains will be analyzed and their genes sequenced, Altinöz said.

Dr. Frank Rühli, director of the Centre for Evolutionary Medicine at the University of Zurich in Switzerland, told Healthline the Turkish brains are a unique find. “Ancient brains are very rare, medically and evolutionarily, even speaking in short terms,” Rühli said.

He said the discovery may be even bigger news to the medical community than to archaeologists. “I am excited and think, theoretically at least, depending on the level of tissue preservation, one could trace degenerative disease, tumors, trauma. etc.,” he said.

In intentionally mummified cadavers found in Egypt, brain tissue remnants have been recovered, but even these samples are rare. “The brain is the most vulnerable organ to post-mortem decomposition…[so] mummifying agents were not always sufficient to preserve brains,” Altinöz said. “Interestingly, in ancient Egyptian civilization, brain tissues were removed during mummification of persons of high social rank.”

The Turkish scientists found other clues that may help explain why the brains they discovered were so well preserved, including extremely high levels of boron in the soil in which the bodies were found.

“Boron exerts anti-bacterial, insect-repellent, and strongly heat resistant efficacies,” Altinöz said. “Interestingly, previous research conducted in Tübingen, Germany revealed that Egyptians intentionally put boron into mummification solutions, based on research in Tutankhamen and Deir el Bahari mummies. The best modern cadaver embalming method is the Thiel’s embalming method, which uses considerable amounts of boron.”

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The elements selenium and tin were not found in the surrounding soil, but they were present in the buried corpses. Nickel and arsenic, which exist naturally in tin mines, and copper also accumulated in the brains. “We concluded that these Bronze Age human specimens also reflected their occupation regarding bronze [making],” Altinöz said. “This study may pave the way to understand very novel pathways of tissue and organ preservation after death, which may even influence the composition of organ-preserving solutions.”